Friction force microscopy of alkylphosphonic acid and carboxylic acids adsorbed on the native oxide of aluminum
Friction force microscopy of alkylphosphonic acid and carboxylic acids adsorbed on the native oxide of aluminum
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DOI：
10.1021/la061082t
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发表时间：
2006-10-24
期刊：
影响因子：
3.9
通讯作者：
McAlpine, Eoghan
中科院分区：
文献类型：
--
作者：
Foster, Trevor T.;Alexander, Morgan R.;McAlpine, Eoghan
用摩擦力显微镜（FFM）、接触角测量和偏振调制红外反射吸收光谱（PM-IRRAS）研究了烷基膦酸（阿帕）和烷基羧酸（ACA）在磁控溅射铝膜上的单分子膜。PM-IRRAS提供的明确证据表明，由FFM数据确定的摩擦系数可能与吸附物分子结构的变化直接相关。摩擦系数随吸附物分子长度的增加而增加，但当吸附物的烷基链中含有8个碳原子时，APA的摩擦系数达到极限值，当吸附物的烷基链中含有12个碳原子时，ACA的摩擦系数达到极限值。对于一个给定的烷基链长度，阿帕单层产生的摩擦系数是类似的单层的烷基硫醇的相同长度，但小于ACA。这些数据表明，阿帕单分子膜比ACA单分子膜更有序。这些推论得到了PM-IRRAS数据的支持，该数据使得能够估计偏置缺陷的密度并与摩擦系数的变化相关联。
Monolayers of alkylphosphonic acids (APA) and alkylcarboxylic acids (ACA) on magnetron-sputtered aluminum films have been investigated by friction force microscopy (FFM), contact angle measurement, and polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS). Clear evidence has been provided from PM-IRRAS that friction coefficients, determined from FFM data, may be correlated directly with variations in adsorbate molecular structure. The friction coefficient increased with the length of the adsorbate molecule, but reached a limiting value when the alkyl chain of the adsorbate contained eight carbons in the case of APA or 12 carbons in the case of ACA. For a given alkyl chain length, APA monolayers yielded coefficients of friction that were similar to those of monolayers of alkylthiols of the same length, but smaller than those of ACA. These data indicate that APA monolayers are better ordered than ACA monolayers. These inferences were supported by PM-IRRAS data, which enabled the density of gauche defects to be estimated and correlated with variations in the coefficient of friction.